1. Field of the Invention
The present invention relates to a holder device that engages two or more members with each other in an axial direction of the members.
2. Description of Related Art
For example, a C-ring as a conventional holder device is described in JP2000-282459A and is used for preventing a target member mounted on a shaft from coming off. Generally, the C-ring is a thin ring-like member having a C shape that is curved along a circumference. When the C-ring is fitted to a target member, the C-ring is deformed in its radial direction. That is, an inner diameter of the C-ring is stretched beyond a shaft diameter of the target member, or an outer diameter of the C-ring is compressed below a bore diameter of the target member. The C-ring by being stretched or compressed in its radial direction is fitted, for example, to a groove that is formed on a shaft of the target member or on an interior wall of a bore of the target member. The C-ring adapts to a shape of the groove by its elastic force, and the body of the C-ring extends beyond the diameter of the shaft to prevent the target member from coming off from the shaft.
Such a C-ring is formed of a material having elasticity. It is necessary to design such a C-ring in a shape that enable the above-mentioned elastic deformation in the radial direction. If a thickness or a cross-sectional area of the C-ring is increased, rigidity of the C-ring rises and elasticity of the C-ring falls. Therefore, to ensure sufficient elasticity, the C-ring is generally designed to have a relatively small thickness and a relatively small cross-sectional area. However, if the C-ring contacts the target member in only a small area, the C-ring will receive any force from the target member in only the small area and the groove of the target member may collapse or the C-ring itself may be damaged, especially when an excessively large thrust force acts upon the C-ring. If hardness of the C-ring is raised by heat treatment and the like, the elasticity of the C-ring falls. Therefore, it is difficult to take effective measures for raising strength of the C-ring without resulting in disadvantages associated with reduced elasticity or the like.
In view of such disadvantages, JP2000-282459A describes an example in which notches are formed on a C-ring having a relatively large cross-sectional area and high rigidity. The C-ring can be elastically deformed at positions where a width of the C-ring is decreased in a radial direction by the notches. However, if such a C-ring is installed in such a position as to be subjected to excessively large thrust forces, it is necessary to apply a heat treatment to the C-ring to raise the surface hardness. However, if the rigidity of the whole body of the C-ring is raised by the heat treatment, the C-ring cannot be easily elastically deformed even at the positions where the C-ring has the notches. Therefore, the C-ring can break at the notches.
JP2000-282459A describes another example in which a C-ring is split into several split keys. The split keys are circularly arranged along a ring-like elastic member. An inner circumferential surface of the ring-like elastic member covers a whole of outer circumferential arc curved surfaces of the split keys. The split keys are fixed on the ring-shaped elastic member. It is possible to fix the split keys on the elastic member after raising rigidity and surface hardness of the split keys. However, in such a conventional C-ring, the inner circumferential surface of the elastic member is intimately fixed on the outer circumferential surface of the split keys. Therefore, the outer circumferential surface of the split keys inhibits deformation of the elastic member. Accordingly, a diameter of the C-ring can be compressed only to a small extent.
Furthermore, if such a C-ring is fitted to a groove of a target member, both of the elastic member and the split keys are in contact with sidewalls of the groove, and are pressed by the target member. Therefore, when the C-ring is subjected to excessively large thrust force, only the elastic member, which has low rigidity, may be plastically deformed. JP2000-282459A describes still another example in which several split keys and elastic members are alternately and circularly arranged. The elastic member is interposed between and thereby connects two split keys adjacent to each other. In such a C-ring, the elastic members are subjected to both of compressive force and tensile force when the C-ring is fitted. Therefore, the elastic members easily break, and can be easily detached from the split keys.